Method for charging non-aqueous electrolyte secondary battery

1. A method for charging a non-aqueous electrolyte secondary battery comprising the step of: repeating pulse charging and charging pause, wherein a pulse charging time is arbitrarily set between a lower limit value and an upper limit value, said lower limit value being an inverse time Tx of a frequency Fx at the high frequency side at which an imaginary part of an alternating current impedance of said non-aqueous electrolyte secondary battery indicates a first local maximum value, or of a frequency adjacent to Fx, and said upper limit value being an inverse time Ty of a frequency Fy at the low frequency side at which an imaginary part of the alternating current impedance of said non-aqueous electrolyte secondary battery indicates a second local maximum value, or of a frequency adjacent to Fy.

2. The method for charging a non-aqueous electrolyte secondary battery in accordance with claim 1 , wherein said frequency adjacent to Fx is within the range of 0.9 Fx to 1.1 Fx, and said frequency adjacent to Fy is within the range of 0.9 Fy to 1.1 Fy.

3. The method for charging a non-aqueous electrolyte secondary battery in accordance with claim 1 , further comprising: measuring an alternating current impedance of said non-aqueous electrolyte secondary battery on a regular or an irregular basis, and correcting said pulse charging time based on the measurement result of the alternating current impedance.

4. The method for charging a non-aqueous electrolyte secondary battery in accordance with claim 3 , wherein the step of correcting said pulse charging time includes: obtaining, from said measurement result of the alternating current impedance, an inverse time Txn of a frequency Fxn at which an imaginary part indicates a first local maximum value, or of a frequency adjacent to Fxn, and obtaining an inverse time Tyn of a frequency Fyn at which an imaginary part indicates a second local maximum value, or of a frequency adjacent to Fyn.

5. A charger comprising: an impedance measurement part for measuring an alternating current impedance of a non-aqueous electrolyte secondary battery; an inverse time calculation part for obtaining, from the result from said impedance measurement part, an inverse time Tx of a frequency Fx at the high frequency side at which an imaginary part indicates a first local maximum value, or of a frequency adjacent to Fx, and an inverse time Ty of a frequency Fy at the low frequency side at which an imaginary part indicates a second local maximum value, or of a frequency adjacent to Fy; a pulse charging time setup part for setting said inverse time Tx and said inverse time Ty as a lower limit value and an upper limit value, respectively, and setting a pulse charging time between said lower limit value and said upper limit value; and a control circuit for controlling charging of said non-aqueous electrolyte secondary battery so as to repeat pulse charging for said set pulse charging time, and pause.

6. The charger in accordance with claim 5 , wherein said control circuit, on a regular or an irregular basis, instructs said impedance measurement part to measure the alternating current impedance of said non-aqueous electrolyte secondary battery, and further, instructs said inverse time calculation part and said pulse charging time setup part to correct the pulse charging time based on the result from said impedance measurement part.